Oil burner system



March .19, 1963 M. A. WEISS OIL BURNER SYSTEM Filed Dec. 1, 1960 llC far/I2 1 I I Malcolm A. Weiss L 7 INVENTOR PATENT ATTORNEY United StatesPatent 3,081,948 01L BURNER YSTEM Malcolm A. Weiss, Union, N.J.,assignor to Esso Re search and Engineering Company, a corporation ofDelaware Filed Dec. 1, 1960, Ser. No. 73,031 5 Claims. (Cl. 239-669)This invention relates to apparatus and methods employed in the burningof hydrocarbons, i.e. to a novel feed system for hydrocarbon burners andto an improved method for controlling the flow of hydrocarbons to acombustion device. This invention is particularly adapted to the burningof liquid hydrocarbons in connection with domestic heating plants.

More particularly, this invention is concerned with novel apparatus andmethods for controlling the air-fuel ratio to a combustion chamber of anoil burner employing venturi atomization.

In conventional combustion devices, fuel and combustion air arecustomarily introduced separately and the resulting mixture subjected toburning in a combustion or flame chamber. In systems of this type theabsence of a direct and continuous control of the fuel to air ratio fedto the combustion chamber often results in large local variations insuch ratio in such chamber causing a needless waste of fuel due toimproper mixing and incomplete combustion with an undesirable incidenceof smoke and attendant hazards unless large amounts of excess air areused.

It is one object of this invention to provide a simplified oil feedsystem that will provide oil burners less sensitive to fuel quality thanconventional gun burners, require a minimum of maintenance and afford amaximum of control of the air-fuel ratio throughout the combustion zone.system capable of effecting efficient smokeless combustion in a minimumof combustion chamber volume. It is another object of this invention toprovide an oil burner system which does not require a high pressure fuelpump as is customarily needed, and to eliminate the customary nozzlewith small passages which tend to clog and erode. It is another objectof this invention to provide a controlled method of feeding oil and airto a combustion chamber which method allows complete modulation at anautomatically controlled constant airfuel ratio. It is a further objectof this invention to provide a device for controlling oil feed to acombustion chamber at a rate dependent solely upon the air flow to suchchamber.

In the instant invention the air to be used in the combustion chamber isblown through an area of converging diameter thereby increasing thevelocity of flow and decreasing static pressure in proximity with a fuelinlet conduit from whence fuel is drawn into the air stream, atomized,and passed with the air through an area of divergence thereby increasingstatic pressure before passage into the combustion zone. Thus, the fuelwhich is introduced in the throat of the venturi is thoroughly atomizedand intimately mixed with the air passing to the combustion zoneassuring eflicient combustion with a minimum excess of air. This in turnallows for a minimum chamber volume for combustion. Fuel is sucked intothe venturi throat through a small feed'line or inlet nozzle line froman auxiliary fuel container. The fuel inlet tube is preferably shaped soas to converge toward the mouth or end emptying into the venturi of themain feed pipe. The minimum area of this convergence, the diameter andlength of the feed line, and the height of the end of this line abovethe liquid level in the auxiliary fuel container are all preferablychosen such that the pressure drop of the oil stream across the con- Itis another object to provide an oil burner 3 ,081,948 Patented Mar. 19,1963 ice vergence is large in comparison with the pressure loss in thefeed line due to friction and in comparison with the pressure due to theliquid head corresponding to the difference in height between the end ofthe line and the level in the fuel container. The fuel container isbackpressured by the air stream static pressure either upstream of theconverging section or downstream of all or most of the diverging sectionso as to essentially equate the pressure drop across the end of the fuelinlet to the pressure drop across the venturi. Since air mass flowvaries as the square root of the venturi pressure drop, and liquid massflow varies as the square root of the pressure drop across the end ofthe fuel line, and these two pressure drops are equal, then the ratio ofair mass flow to fuel mass flow must be constant for any reasonable airmass flow. Therefore, by varying the rate of air supply, for example byvarying the air blower speed, modulation results with automaticallyconstant air/fuel ratio.

Fuel may be supplied to the auxiliary fuel container either by gravityfeed or by a low-pressure fuel pump which may be clutch-coupled to theair blower shafts. It is only necessary to maintain a small head ofliquid in the container.

At or near the end of the venturi, immediately before entry of theair-fuel mixture into the combustion chamber, means are preferablyprovided for returning to the auxiliary fuel container liquid fuel thatmay be deposited on the walls of the venturi. This means may consist ofa circular slot, rim, or porous or perforated section in the wall of theventuri whose bottom-most part is connected by a return line to the fuelcontainer. This line may also serve to back-pressure the fuel in thecontainer.

The invention will be more easily understood by referring to theaccompanying drawings.

FIGURE 1 represents a semi-diagrammatic illustration of one embodimentof the inventive feed system wherein the fuel inlet is directedperpendicular to principal direction of air flow and positioned nearerto the combustion chamber thanto the blower or other air pressuringdevice.

FIGURE 2 represents a modificationof the feed system of FIGURE 1 whereinfuel inlet is directed parallel to the principal direction of air flowand positioned nearer to the blower than to the combustion chamber.

In FIGURE 1, an air driving means or blower 10, eg. a motor driven fanenclosed in a housing, communicates with a main feed tube so as to admitof a flow of air from blower 10 through the enclosure formed by tube 11.The tube 11 comprises a venturi tube, i.e. a tube converging through afirst extension 11A toward a length or point of constriction, the throatof the venturi 1115, which in turn leads into a diverging extension 11C.At the end opposite blower 10 tube 11 empties into a combustion chamber,not shown. At the throat of the venturi is positioned fuel inlet tube 12which communicates with auxiliary fuel tank 13. Fuel is introduced intotank 13 via pipe 14. Gravity feed through pipe 14 is controlled by afloat valve 15. Optionally a low pressure fuel pump may be employed, ifdesired. Air driven by blower 10 through tube 11 upon passing intoventuri throat 11B is accelerated in velocity resulting in a decrease instatic pressure causing fuel to be sucked from fuel inlet tube 12 intothe air stream passing through throat 11B where such fuel is atomized,intimately mixed with such air stream and carried on into the combustionchamber. Any excess fuel entering throat -11B which is not atomized andcarried out by the air stream is returned by tubes 16 and 17 which inturn communicate with fuel tank 13 and may in addition serve as apressure balance mechanism for the entire feed system.

FIGURE 2, which illustrates a preferred embodiment of the invention, isa modification of FIGURE 1 demonstrating the flexibility of designwithin the scope of this 3 invention. In FIGURE 2, a fuel collectingslot 19 about the interior wall of tube 11 is shown feeding into fuelreturn tube 16.

In operation, such a device may be designed to provide for oil feedrates in the range of about 0.1 to 2 gallons per hour. If the oil feedline converges at its exit, the minimum inside diameter of theconvergence should be 1 to 15% of the diameter of the throat of theventuri, and preferably 3 to 7%. Additionally, this minimum diametershould be no larger than one-third of the inside diameter of the oilfeed line, which is preferably in the range of to A. The length of theoil feed line should be as short as practicable, preferably notexceeding 2 feet. The exit of this line should be at least one inch butpreferably not more than 12 inches above the oil level in the auxiliaryfuel container.

The air velocity in the throat of the venturi is preferably in the rangeof 150 to 500 feet/sec. but may extend outside of this range if higherdegrees of modulation are necessary. The diameter of the throat is suchthat, at these velocities, at least enough mass of air will be passed tocombine stoichiometrically with the oil fed but preferably not enough toexceed 150% of the stoichiometric requirement. In regard to rates anddegrees of convergence and divergence, the venturi should be designed inaccordance with the well-known standards of good practice. Introductionof the fuel line into the venturi should cause the minimum practicableobstruction and disturbance of the air flow.

The following example is offered for purposes of illustration and shouldnot be considered as a limitation upon the true scope of the inventionas set forth in the claims.

Example I A fuel feed system designed in accordance with FIG- URE 2 isconnected with a combustion chamber. The air driving means is powered todeliver about 1500 standard cubic feet of air per hour through a throatdiameter of about 0.5 inch at a throat velocity of about 300 feet/ sec.The total pressure requirement from the air driving means is equivalentto about 4 inches H O above atmospheric pressure and the theoreticalpower required for air compression is about 0.015 horsepower. The fueloil, typically a No. 2 heating oil with a specific gravity of about0.85, is drawn into the venturi throat from a fuel line with a minimuminner convergence diameter of about 0.025 inch under the aboveconditions at a firing rate of about 1 gallon per hour. The pressuredifferential between the surface of the fuel in the fuel container andthe throat of the venturi is about 18 inches H O. Operating under theabove described conditions, the fuel oil is delivered in a spray to thecombustion chamber with a mass median drop size of about 20-40 microns.

This demonstrates advantages afforded by the feed system of thisinvention in the following particulars: First, the power requirementsare such that the motor for driving the air fan could be smaller thanthose employed in conventional systems. Note there would be no motorload resulting from fuel pumping requirements at the usual highpressures. Second, the atomization effected, which is more than adequatefor clean burning in view of the good air fuel mixture, could beimproved to afford even smaller drop sizes by an increase in throatvelocity. Third, the excellent control of fuel/ air ratio and mixingallows use of a smaller combustion chamber than usual Without loss ofefiicient smokeless burning. Third, the venturi would automaticallyreduce startup and shutdown smoke without employing a clutch on themotor since the oil is not delivered to the venturi throat unless theair velocity is brought near to the normal operating level. Fourth,there are no rotating parts other than the air blower and no smallpassages in the fuel line to clog or erode so that maintenance andreplacement of parts are minimized. Fifth, the air/ fuel ratio can beheld constant automatically at varying air rates. Thus, the burneroutput can be modulated by simply changing the air rate withoutdisturbing this ratio. Finally, any problem of droplet deposition on theventuri walls is easily handled by a collecting slot and oil return linewhich can also be employed to effect pressure balance.

What is claimed is:

1. An apparatus for feeding an oil and air mixture to a combustion zone,said apparatus comprising (1) a feed tube of varying internal diameterhaving a first end, a second end of inside diameter approximately thesame as that of said first end, and a constricted region intermediateits first and second ends of inside diameter appreciably smaller thanthat of either of its ends, the internal surface of said tube convergingsmoothly from its first end to its constricted region and divergingsmoothly from its constricted region to its second end, and said tubebeing connected at its second end to a combustion zone, (2) a closedvessel for holding an oil supply, said vessel being not more than asmall distance below the constricted region of said feed tube, (3) meanscommunicating with said vessel for maintaining a supply of oil therein(4) an oil conduit having an inlet end communicating with said vesselnear the bottom thereof and an outlet end communicating with said feedtube within the constricted region thereof, said conduit having agenerally uniform inside diameter but converging locally internallytoward its outlet end to an inside diameter thereat which is not lessthan 1% and not more than 15% of the inside diameter of the constrictedregion of said feed tube, and not more than one third of its owngenerally uniform inside diameter, (5) pressure balance conduit meanshaving one end communicating with said vessel near the top thereof andat least one other end communicating with said feed tube at a pointclosely adjacent one of the ends of said tube, and (6) air blowing meansconnected to said feed tube at the first end thereof and adapted todischarge air into said tube at its first end.

2. An apparatus according to claim 1 in which the inside diameter ofsaid oil conduit at its outlet end is not less than 3% and not more than7% of the inside diameter of the constricted region of said feed tube.

3. An apparatus according to claim 1 in which the generally uniforminside diameter of said oil conduit is not less than inch and not morethan inch.

4. An apparatus according to claim 1 in which the length of said oilconduit is not more than 2 feet.

5. An apparatus according to claim 1 in which said means communicatingwith said vessel for maintaining a supply of oil therein is adapted tomaintain that supply at a controlled level, and the outlet end of saidoil conduit is not less than 1 inch and not more than 12 inches abovethat level.

References Cited in the file of this patent UNITED STATES PATENTS980,801 Kraus Ian. 3, 1911 1,208,341 Loftus Dec. 12, 1916 1,267,760 GoodMay 28, 1918 1,820,774 Boyce Aug. 25, 1931 1,875,729 Hermann Sept. 6,1932 2,267,451 Eweryd et al. Dec. 23, 1941 2,589,559 Lebeda Mar. 18,1952 2,861,838 Wyatt et al Nov. 25, 1958 FOREIGN PATENTS 12,808 GreatBritain 1913 415,733 Great Britain Aug. 27, 1934 957,200 France Aug. 22,1949

1. AN APPARATUS FOR FEEDING AN OIL AND AIR MIXTURE TO A COMBUSTION ZONE, SAID APPARATUS COMPRISING (1) A FEED TUBE OF VARYING INTERNAL DIAMETER HAVING A FIRST END, A SECOND END OF INSIDE DIAMETER APPROXIMATELY THE SAME AS THAT OF SAID FIRST END, AND A CONSTRICTED REGION INTERMEDIATE ITS FIRST AND SECOND ENDS OF INSIDE DIAMETER APPRECIABLY SMALLER THAN THAT OF EITHER OF ITS ENDS, THE INTERNAL SURFACE OF SAID TUBE CONVERGING SMOOTHLY FROM ITS FIRST END TO ITS CONSTRICTED REGION AND DIVERGING SMOOTHLY FROM ITS CONSTRICTED REGION TO ITS SECOND END, AND SAID TUBE BEING CONNECTED AT ITS SECOND END TO A COMBUSTION ZONE, (2) A CLOSED VESSEL FOR HOLDING AN OIL SUPPLY, SAID VESSEL BEING NOT MORE THAN A SMALL DISTANCE BELOW THE CONSTRICTED REGION OF SAID FEED TUBE, (3) MEANS COMMUNICATING WITH SAID VESSEL FOR MAINTAINING A SUPPLY OF OIL THEREIN (4) AN OIL CONDUIT HAVING AN INLET END COMMUNICATING WITH SAID VESSEL NEAR THE BOTTOM THEREOF AND AN OUTLET END COMMUNICATING WITH SAID FEED TUBE WITHIN THE CONSTRICTED REGION THEREOF, SAID CONDUIT HAVING A GENERALLY UNIFORM INSIDE DIAMETER BUT CONVERGING LOCALLY INTERNALLY TOWARD 